Include pre-receive blob size in SaaS analytics
Proposal
As discussed in this slack thread it would be very helpful for traffic profiling to collect blob sizes during pre-receive push. This would better inform us around what our p99/90/50 blob sizes are, what our peak traffic looks like, and other metrics for modifications to the pre-receive logic, including Category:Secret Detection
Following a similar approach to !128936 (merged) should get us close